I can see a system where the educator keeps sort of an internal gradebook and simply work with improving skills until the final grade is levied at the end based on mastery.
“No grades at all” runs up against the problem of intrinsic/extrinsic motivation, I’d think. As well as the issue of college admissions, which are going to demand some sense of placement over and above the SAT exams.
This is a system which is working very well in a lower (not low, but lower) income area in Houston, nearly 100% minority (but with a high percentage of Asians). Basically, the students self-select by applying to go to the school; their middle school counselors have to certify that they are self-driven learners that will succeed without formal classes or structure.
The problem is most of the students don’t self-select, because there are no sports, and it has a reputation for being extremely rigorous. That said, it continues to be one of the best schools in the metro area despite it’s difficult demographic.
How does it work? Teachers give the students a series of self-learning packages each of which are due days or weeks after issuance. No (or few) formal classes, teachers are available in resource centers if the students require assistance. The packages are graded and there is testing.